A method of switching a communication channel when a mobile station moves from one service area to another service area is disclosed. The mobile station determines a difference between the transmission phase of a frame synchronizing signal received from a first base station currently holding a communication channel with the mobile station and the transmission phase of a frame synchronizing signal received from a second base station expected to newly set up a communication channel with the mobile station. The mobile station sends phase difference information representative of the above difference to the first base station via the communication channel. The first base station having received the phase difference information transfers the information to the second base station, causing it to correct the phase of data thereof to be sent to the mobile station. This successfully implements soft handover while guaranteeing the phase synchronization of frames sent from the two base stations.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for use in controlling switching of a communication channel when a mobile station located in a first service area moves to a second service area adjoining the first service area, said method also for use with a mobile communication control center and a plurality of base stations, each of which is capable of setting up a communication channel with the mobile station for interchanging communication data and for controlling communication channel switching to be effected between two or more of the plurality of base stations and for multicasting the communication data to the two or more base stations to which the communication channel may be switched, said method comprising: decomposing the communication data, which are to be multicast, into decomposed data having a unit time interval shorter than a frame length; adding an unconditional identification code to each of the decomposed data; determining, with a first base station holding a communication channel with the mobile station, leading data of a next frame period in consideration of a second base station expected to newly set up the communication channel; and sending an identification code corresponding to the leading data to the second base station before the second base station sets up the communication channel.
2. A method for use in controlling switching of a communication channel when a mobile station located in a first service area moves to a second service area adjoining the first service area, said method also for use with a mobile communication control center and a plurality of base stations, each of which is capable of setting up a communication channel with the mobile station for interchanging communication data and for controlling communication channel switching to be effected between two or more of the plurality of base stations and for multicasting the communication data to the two or more base stations to which the communication channel may be switched, said method comprising: determining, by the mobile station, a difference between a transmission phase of a frame synchronizing signal received from a first base station currently holding a communication channel with the mobile station and a transmission phase of a frame synchronizing signal received from a second base station expected to newly set up a communication channel with the mobile station; sending phase difference information, representative of the difference between the transmission phase of the frame synchronizing signal received from the first base station and the transmission phase of the frame synchronizing signal received from the second base station, from the mobile station to the first base station via the communication channel; transferring, by the first base station which received the phase difference information, the phase difference information to the second base station so as to cause the second base station to correct a phase of data to be sent from the second base station to the mobile station; decomposing the communication data, which are to be multicast, into decomposed data having a unit time interval shorter than a frame length; adding an unconditional identification code to each of the decomposed data; determining, with the first base station holding a communication channel with the mobile station, leading data of a next frame period in consideration of a second base station expected to newly set up the communication channel; and sending an identification code corresponding to the leading data to the second base station before the second base station sets up the communication channel.
3. A method of controlling switching of a communication channel in a mobile communication system, comprising: preparing a plurality of base stations, each forming a service area, adjoining each other for setting up a communication channel with a mobile station and for transmitting and receiving communication data to and from the mobile station; preparing a mobile communication control center for controlling the plurality of base stations to switch the communication channel between two or more of the plurality of base stations; decomposing communication data, which are to be multicast, into pieces of data which have a unit time interval shorter than a frame length and allotting a specific identification code to each of the pieces of data to form multicasting data; multicasting the multicasting data from the mobile communication control center to two or more base stations to which the communication channel with the mobile station may be switched; determining, by a first one of the base stations which currently holds the communication channel with the mobile station, a leading one of the pieces of data of a following frame period in consideration of a second one of the base stations which is expected to newly set up the communication channel with the mobile station; and sending an identification code allotted to the leading piece of data from the first base station to the second base station prior to switching the communication channel with the mobile station from the first base station to the second base station, wherein the communication channel with the mobile station is switched from the first base station to the second base station while the mobile station moves from one to another of the service areas adjoining each other and formed by the first and second base stations.
4. A method in accordance with claim 3, further comprising: determining, by the mobile station, a difference between a transmitted phase of a frame synchronizing signal received from the first base station and a transmitted phase of a frame synchronizing signal received from the second base station; sending phase difference information representative of the difference determined from the mobile station to the first base station over the communication channel; receiving the phase difference information by the first base station; transferring the phase difference information from the first base station to the second base station; and correcting, by the second base station, a phase of data to be transmitted from the second base station to the mobile station.
5. A method in accordance with claim 3, wherein the pieces of data are miniframes to each of which a time stamp is added.
6. A method in accordance with claim 5, wherein the identification code includes a number of the miniframe.
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October 22, 1997
July 10, 2001
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